The invention relates to an apparatus for anchoring self-supporting tall structures such as masts, towers or the like in a foundation.
Such tall structures have been anchored to foundations in different ways. For example, it is possible to secure or clamp these tall structures rigidly in the foundation. However, it has been found in connection with tall masts used for wind-driven power generators, that damage to the foundation occurs after a short operational period due to the dynamic loads. Such dynamic loads in this instance, for example, are due to the wind forces or due to vibrations transmitted from the propeller to the wind-driven power generator.
Further, it is also possible to secure such structures by stay wire means. However, this again results in problems with the wires, the wire heads, the pivotal wire connections and the foundations for the wire anchoring. Besides, stay wire means require a substantial space so that in connection with the wind-driven power generator, for example, problems may occur with the free operation of the propeller since it is absolutely necessary to avoid any interference between the free rotation of the propeller and the stay wires. Further, the high tension of the wires or cables must be taken up by the foundation of the tall structure. Extremely high additional normal forces or loads therefore may occur due to the vertical components of the tension forces in the wires or cables.
German Patent Publication (DE-OS) No. 2,450,064 discloses the self-supporting elastic clamping of parking meters, road or street signs, street lighting masts, flagposts or fence posts in a foundation. As compared to a rigid clamping, such an elastic clamping has the advantage that the structure cannot easily break off. According to said prior art as disclosed in German Patent Publication No. 2,450,064, the post or mast is inserted into a tubular bore of the foundation whereby a bushing of elastic material is arranged and the upper edge of the bore and the bushing is anchored in the foundation.
A sleeve which grips the post or mast is pressed in position between the bushing on the one hand and the post or mast on the other hand. Thus, the bushing is compressed by about 30% of its volume. However, the combination comprising the bushing and sleeve remains elastic within certain limits. The reference does not disclose anything further regarding supports for tall posts or masts.
The self-supporting, tall structures to which the invention particularly pertains are, for example, masts for wind-driven power generators. Such masts may presently reach heights of more than 100 meters in certain instances and carry a rotor at the tip of the mast. The rotor is wind driven as well as operatively connected to a generator. The forces effective on such structures are caused on the one hand by the wind which is effective on the mast and the rotor, thereby causing buckling loads and bending loads on the mast. Further, dynamic forces occur additionally and these dynamic forces may also be due to the wind but also due to the transmission of the vibrations of the rotor onto the mast. These forces in turn may cause vibrations of the mast which may correspond to the resonance frequencies of the mast or they may correspond to an interference between these frequencies and the frequencies of other system vibrations. If one takes into account that the tip of the mast of such wind-driven power generators may perform pendal motions of several meters in response to the corresponding forces effective on the mast, it will be appreciated, that a substantial importance attaches to the support of the mast.